1. Technical Field
This invention relates generally to alternators for internal combustion engine applications and the like and to methods of manufacturing such alternators, and further to the manufacture of molded plastic housings for electrical devices generally having a bearing for supporting a rotating shaft.
2. Related Art
Alternators, particularly those for automotive engine applications, are fabricated with drive-end (D.E.) and a stator-regulator-end (S.R.E.) frames which house a stator and rotor and support the other components that make up the alternator. The stator is normally fitted in the D.E. frame. Both frames are typically cast from aluminum and have several surfaces that require secondary machining to prepare the surfaces to support a corresponding component of the alternator. One of those surfaces is the stator bore of the D.E. frame which supports the stator. Once machined, the D.E. frame is heated to expand the stator bore at which point the stator is inserted into the D.E. frame and the frame then cooled to shrink the D.E. frame about the stator to retain the stator in place. The machining and heating operations add to the cost of manufacturing such alternators.
Aluminum is typically employed for the D.E. frame for its ability to provide a ground path for the stator and for its strength and dimensional stability at elevated operating temperatures of the stator.
Included among the other machined surfaces of such aluminum D.E. frames is a bearing well whose inner surface is machined to receive a sealed D.E. roller bearing with a press fit. The well includes a lip of aluminum material extending about the opening of the bearing well which, after installation of the bearing, is spun over onto the outer race to capture the bearing axially within the well. The secondary machining and lip deformation operations further add to the cost of alternators. Moreover, when it is desired to rebuild a spent alternator, the spun-over lip must be ground off and the D.E. frame modified with a retro-fit metal retainer fastened to the bearing well in position of the former spun-overlip. Such process involves remachining of the bearing well wall, removal of the spun-overlip and machining of the frame to receive the retainer ring, and the provision and fastening of the retainer ring to make use of the otherwise spent, aluminum D.E. frame. Such adds cost to the rebuilding of spent alternators.
Other surfaces that require machining are the mating surfaces of the D.E. and S.R.E. frames, which are brought together and then secured by fasteners. Also machined are several bores which are fitted with pressed steel bushings for mounting the alternator in service. Such dissimilar metal materials (i.e., steel against aluminum) present issues of corrosion which must be contended with.
U.S. Pat. No. 4,705,983 discloses an alternator having, as part of its structure, an end shield fabricated of insulating plastics material and formed with a central molded hub that, after forming, is provided to seat a roller bearing.
U.S. Pat. No. 5,982,057 discloses molding a plastics housing in place about a stator of an electric motor along with a molded-in bearing bush. Following molding, a roller bearing is installed in the bearing bush. Provision of the molded-in bearing bush adds cost and complexity to the structure.
It is an object of the invention to overcome or greatly minimize the foregoing limitations in connection with alternators and other electrical devices employing a plastic housing to support a bearing of the art.
According to one aspect of the invention, an alternator is provided comprising a D.E. frame having an electrical grounding portion; a stator secured to the D.E. frame remote from the grounding portion; a D.E. bearing secured to the D.E. frame; a S.R.E. frame secured to the D.E. frame, a S.R.E. bearing secured to the S.R.E. frame, a rotor housed within the D.E. and S.R.E. frames and journaled by the D.E. and S.R.E. bearings for rotation relative to the rotor, and wherein the D.E. frame is fabricated of plastics material and includes an electrically conductive ground circuit coupling the stator electrically to the ground portion. This aspect of the invention has the advantage of providing a plastics D.E. housing which is less costly and lighter weight than the aluminum counterparts and yet is provided with a ground path for the stator.
According to a further aspect of the invention, a housing assembly, such as the D.E. or S.R.E. frame of an alternator, includes a sealed roller bearing having inner and outer races and roller elements therebetween, and a molded plastics housing having a bearing well within which the sealed roller bearing is molded in place. The bearing well includes an inner wall surface engaging an outer surface of the outer race, and axial restraining portions which extend radially inwardly from the inner wall of the well in overlying relation to axially opposite end faces of the outer face for restraining the bearing axially against removal from the bearing well. According to a related method of the invention, during molding, the bearing is maintained at a temperature in the mold below that which would cause heat damage to the bearing. This aspect of the invention has the advantage of providing a simple, effective way of securing a sealed, heat-sensitive roller bearing within a housing, such as an alternator frame, which avoids machining or pressing operations or provision of a premolded bearing bush. The same technique and features are applicable to other plastics housings of electrical devices in which the bearing is molded in place in the housing.
According to yet another aspect of the invention, an alternator is formed according to a method in which the D.E. frame is molded from plastics material and is removed from the mold. While still hot, the stator is installed in the D.E. frame and the plastics material allowed to cool to constrict about the stator to secure the stator in place in the D.E. frame.
According to still a further aspect of the invention, a ground path is molded in place in a plastic housing of an electrical component to establish a defined electrical path through the plastics housing.